The present invention relates in general to underwater communications over cables and, more particularly, to an articulated cable riser system including modular anchors and modular buoys.
Many underwater operations require communications over cables extending between the floor of a body of water, generically referred to herein as a sea, and the surface of the sea. A surface station, such as a ship, moves due to waves, wind and currents. To prevent the cable from being damaged by such motion, the end of the cable which is anchored to the sea floor must be isolated from the surface station.
In existing undersea cable installations, one or more groups of anchors, referred to as "clump" anchors, have been secured to an end or portion of the cable which is to be secured to the sea floor. To provide a slack loop, referred to as a wave, in the cable as it extends from the sea floor to the surface and thereby accommodate motion of the surface station, a group of mid-span buoys, referred to as "clump" buoys, have been secured to the cable some distance above the sea floor to form what is referred to a lazy-S riser. Alternately, distributed buoyancy modules, which are spaced from one another and individually secured to the cable, have been used.
Unfortunately, the clump anchors, clump buoys and distributed buoyancy modules cannot be secured easily to the cable prior to deployment of a cable making their installation time consuming and difficult. Since the clump anchors, clump buoys and distributed buoyancy modules must be secured to the cable as the cable is being installed, they cannot be deployed and recovered using conventional cable laying equipment. Further, installation of a cable using these anchors and buoys usually requires two ships and can result in cable damage due to exceeding the minimum bend radius and/or overtensioning as the result of ship motion in rough seas and/or miscommunication between deck hands and crane operators when two ships are used.
It is, thus, apparent that there is a need for an improved underwater cable riser system which would overcome the problems presented by the current use of clump anchors, clump buoys and distributed buoyancy modules in undersea cable riser installations. Preferably, the improved underwater cable riser system could be rapidly installed on a cable, permit pre-assembly of anchors and buoys to cables to be deployed, and be deployable and recoverable using conventional cable laying equipment for faster installation and recovery.